1. Field of the Invention
This invention relates to a metal mold for manufacturing amorphous alloy and a molded product of amorphous alloy.
2. Description of the Related Art
Recently, amorphous alloys having very low critical cooling rates of 1 to 100 K/s have been developed. These are, for example, amorphous alloys of Zr--Al--Co--Ni--Cu system, Zr--Ti--Al--Ni--Cu system, Zr--Ti--Nb--Al--Ni--Cu system, Zr--Ti--Hf--Al--Co--Ni--Cu system, Zr--Al--Ni--Cu system, etc. And, accompanying these alloys, large (bulk) molded products of amorphous alloy are being produced with various methods. These methods are, for example, forging method in which molten metal is pressed and formed into a predetermined configuration, rolling method in which molten metal is rolled, and casting method in which molten metal is casted into a predetermined configuration. Conventionally, in a metal mold for manufacturing large molded product of amorphous alloy with these methods, it is thought that crystalline core tends to generate at contact points of the molten metal and the metal mold when the molten metal solidifies without high smoothness of the metal mold. Therefore, an inner face of the metal mold, which contacts the molten metal, is polished to be extremely smooth.
However, even an amorphous alloy having very low critical cooling rate, to obtain a large molded product, needs high cooling rate as a whole. On the other hand, to obtain a thin and large plate-shaped molded product, the molten metal has to retain liquidity until completely filled in a cavity portion of the metal mold. Therefore, it is necessary to deliberately set heat conductivity of the metal mold, and control cooling state of the metal mold. However, it is extremely difficult for a necessary condition that the molten metal must be cooled at over the critical cooling rate, and obtaining a molded product of amorphous alloy having large area is very difficult.
Further, in cooling simultaneously with molding, cold shuts are generated by contact of cooled surfaces, and in case that newly poured molten metal of high temperature contacts a cooled amorphous area, the cooled amorphous area is heated and crystallized, the molded product does not totally consist of amorphous phase, and has very bad characteristics. Therefore, it is necessary to control flow of the molten metal to prevent the cooled surfaces from contact. However, there is no time to regulate (control) the flow of the molten metal, because cooling immediately starts when the molten metal flows into the cooled metal mold.
It is therefore an object of the present invention to provide a metal mold for manufacturing amorphous alloy with which a thin and large plate-shaped molded product is obtained, and a molded product of amorphous alloy having excellent strength characteristics.